While ideal quantum key distribution (QKD) systems are well-understood, practical implementations face various vulnerabilities, such as side-channel attacks resulting from device imperfections. Current security proofs for decoy-state BB84 protocols either assume uniform phase randomization of Alice's signals, which is compromised by practical limitations and attacks like injection locking, or rely on a (partially) characterized phase distribution. This work presents an experimental method to characterize the phase de-randomization from injection locking using a heterodyne detection setup, providing a lower bound on the degree of isolation required to protect QKD transmitters against injection-locking attacks. The methods presented are source-agnostic and can be used to evaluate general QKD systems against injection-locking attacks.
@article{arxiv.2412.10290,
title = {Evaluation of quantum key distribution systems against injection-locking attacks},
author = {Jerome Wiesemann and Fadri Grünenfelder and Ana Blázquez and Nino Walenta and Davide Rusca},
journal= {arXiv preprint arXiv:2412.10290},
year = {2025}
}